El Niño Southern Oscillation index: duration and intensity of La Niña and El Niño years. El Niño is usually defined as a positive temperature anomaly in the east and central tropical Pacific. Another way to express the climate phenomenon is through an index (Southern Oscillation index) for air pressure difference across the equatorial Pacific – with relatively high pressure in the West and low pressure (because of increased convection over warm water) in the East typical for El Niño. The above graph uses that alternative indicator – and it holds a clue to our temperature predictions for 2014 and 2015: hottest year on record, followed by the hottestest year on record…

The second half of 2014 may bring Pacific temperature anomalies of more than 1.5 degrees Celsius, lifting global average temperatures – and increasing the net likelihood of extreme weather events across the globe. The 2014 average temperatures will quite likely be sufficiently lifted above the global temperature trend to create a new global temperature record – and delayed oceanic and atmospheric effects will likely increase that warming over much of 2015, thereby creating two subsequent ‘hottest years on record’.

How much is +0.2C + +0.2C? Probably enough to bring the two hottest years ever measured – in a row.

Many recall the powerful El Niño event of 1997-1998. If you live in California that is because of the continuous downpours – if you live in South East Asia it’s because of the intense smog of the Borneo wildfires. If you are a climate geek you will know these wildfires contributed an estimated 40 percent extra CO2 (additional to fossil fuel emissions) to the atmosphere, caused by prolonged drought in the West Pacific.

Climate geeks also know that 1998 turned out to become a sursprisingly hot year – right up there with the other two really hot years that followed in the next decade: 2005 and 2010.

In fact as shown in the graph of the NASA GISS land-ocean temperature dataset below – that single El Niño event was so powerful, it created a +0.2 degrees Celsius temperature anomaly (on top of the 30-year average trend).

temperature trend for El Niño, La Niña and neutral years, up to 2013, based on NASA GISS dataset.

It’s a fantastic graph as it shows many other things. One is that also much weaker El Niño years tend to lift temperature above the climatic average (just like La Niña years fall below that average) and another is how that average is increasing over decades and years. The climate average temperature is in 2014 some 0.2 degrees warmer than 16 years ago, in 1998.

Indeed, that means that any year with a positive temperature anomaly – that is a year that peaks above the trend line – will now almost automatically break the world temperature record (depending on prefered dataset any of the years 1998, 2005 and 2010).

Judging by the same graph a weak El Niño should be able to do the trick. Thus far we’ve had near neutral ENSO conditions in 2014 – and monthly average temperatures more or less in line with that. We will have at least a weak to moderate El Niño from June onwards – possibly strengthening in northern hemisphere autumn. Combining these two half years – and noting the absence of any predictable disturbing factor, like a solar minimum – we are not the first to conclude that 2014 is likely to break the world temperature record – and become the hottest year ever measured.

At this point is becomes interesting though to again look at the first graph, at the top of this article. It shows El Niño events can be short-lived and strong, or long-lived and weak. And most of the time the global temperature effects can come a bit delayed…

Record-hot years 2005 and 2010 for instance were hardly El Niño years – they were however El Niño-influenced years: the 2005 temperature record followed El Niño that occurred between mid-summer 2004 and the winter of 2004-2005. The same goes for 2010, although that (very weak!) El Niño lasted into the spring months of 2010 – to be followed by a rather powerful La Niña that could however not prevent yet another hot year [the hottest thus far according to NASA GISS]. The same goes for hot years 2007 and 2003. El Niño had more or less ended at the start of these years, that still turned out to become hot anomalies.

The most interesting comparison however is of course with that very powerful 1997-1998 El Niño. It had started somewhere in May of 1997 and ended almost a ful year later, around April 1998. Globally 1997 indeed turned out to be relatively warm (>0.05C above average) – but the subsequent year was almost four times as hot.

And that, to go short, is statistically the most logical thing to expect if the approaching El Niño would reach at least moderate strength (as forecast) – and continu through the second half of the year (as most models indicate): the average global temperature will be lifted enough for a new global record in 2014 (as anything close to +0.05C would likely do that trick) and 2015 is then likely to immediately break that record and become even hotter – caused by delayed El Niño effects, and of course an ever-rising temperature trend, in line with ever-rising atmospheric CO2-concentrations.

Disclaimer: the unexpected eruption of a Mount Pinatubo-like explosive tropical volcano. Other than that (as solar activity for 2014-2015 is also forecast to be normal to high): expect two unprecedentedly hot years – and be warned for possibly a lot of El Niño-related extreme weather events.